1. Field of the Invention
The present invention relates generally to coil tubing injection and retrieval and, specifically, to methods and apparatuses for injecting and retrieving tubewire into or out of coiled tubing.
2. Description of the Related Art
In hydrocarbon wells, it is typically necessary to supply electrical power and signals downhole to control various tools and/or collect data. One way to achieve this is by inserting wireline into a coiled tubing and then running the coiled tubing and wireline into the well to a desired location. In general, wireline is a braided steel cable with several layers of armor having conductors inside. Once the wireline is run downhole, an electric current or signal may be applied to the wireline in order to activate the downhole tool, or the wireline may be used to collect and transmit data downhole.
There are a number of techniques used to insert the wireline into the coiled tubing. In one technique, the coiled tubing is stretched out along a surface, and the wireline is pumped or pulled through the coiled tubing. In another, the coiled tubing is run into a well and the wireline is injected. Lastly, the most commonly used method involves injecting the wireline into coiled tubing wrapped onto a reel using a capstan injector. Here, a capstan drum is housed within a high pressure housing, and the wireline is fed into the housing, wrapped around the drum several times and, then, is fed into the coiled tubing via a flow tube. Fluid, normally water, is pumped through the flow tube and through the coiled tubing until the wireline is injected.
High drag forces are present during the capstan injection technique. The flow tube has a small internal diameter so that when the fluid is pumped through it, high velocity is generated which creates a high drag force on the wireline. This force is used to pull the wireline through the tube and into the coiled tubing. The force also creates tensions on the wireline as it is wrapped around the drum, thus allowing the capstan effect to work. The rotating drum in the capstan injector, plus the capstan multiplier effect, is enough to pull the wireline off the reel and against the high pressure into the capstan injector. The fluid being pumped through the coiled tubing continues to drag the wireline along until it is injected.
There are a number of problems associated with the wireline techniques. First, depending on the fluid pumped, the wireline can be damaged. For example, if acidic fluid is used, the wireline becomes damaged over time. Second, the wireline requires in-field maintenance due to the fact the amount of wireline slack within the coiled tubing needs to be controlled and adjusted over the life of the string, which is an awkward and time consuming procedure. Third, due to the relatively large outside diameter and high roughness of the wireline, there is a significant increase in pumping pressure or loss of pump rates associated with coiled tubing strings containing wireline. Fourth, it is difficult to install wireline into long lengths of coiled tubing due to the high pumping pressures required to do so using the capstan injector, or due to the difficulty in finding a deep well or long unobstructed surface that might otherwise be required. Last, the wireline is not durable in the long run since it is susceptible to kinking and birdnesting if not cared for properly.
There is another product currently available, known as tubewire, which may be used to provide power and data communication downhole. In general, a tubewire consists of a tube containing an insulted wire and may come in various sizes. An example is the tubewire manufactured by Canada Tech Corporation of Calgary, Canada.
Tubewire provides a number of advantages over braided wireline. First and foremost, is the tube completely encases the wire and protects it from fluid and mechanical damage. Second, tubewire is more durable than wireline, in that tubewire is compatible with a larger variety of pumping fluids. Third, tubewire requires minimal maintenance. Fourth, unlike wireline, tubewire has a small diameter and a smooth surface resulting in little increase in pumping pressure or loss of pump rate. Last, long lengths of tubewire can be injected into a reel of coiled tubing and, therefore, a deep well or long level surface is not required.
Wireline capstan injection techniques, however, will not work with tubewire for several reasons. First, the tubewire is quite stiff relative to its diameter and, thus, would be very difficult to bend and hold tight against the capstan drum. Second, large forces would be required to hold the tubewire tight against the drum and the flow tube would not be able to create such forces without generating unmanageable pressures. Last, the flow tube would need to be long and would require a very small clearance between the inner diameter of the flow tube and the outer diameter of the tubewire; however, since the tubewire is stiff, and it will have a residual curvature: these two aspects will result in high friction drag through the flow tube, thereby creating even more unmanageable pressure induced forces. Moreover, injecting the tubewire using the other wireline methods is impractical and expensive.
In view of these disadvantages, there is a need in the art for an improved injection and retrieval method utilizing a tubewire, and being adapted for use while the coiled tubing is on a reel, thereby providing a more cost efficient injection and retrieval method which supplies a more durable downhole electrical/communication means.